The present invention pertains to a hardenable, fluorinated copolymer of vinylidene fluoride (C.sub.2 H.sub.2 F.sub.2), at least one fluorinated monomer selected from tetrafluoroethylene (C.sub.2 F.sub.4), chlorotrifluoroethylene (C.sub.2 F.sub.2 Cl) or hexafluoropropylene (C.sub.3 F.sub.6), and an acrylamide derivative. This copolymer, which is soluble in organic solvents, is particularly recommended for the manufacture of paints and varnishes.
Fluorinated polymers are known for their good mechanical properties and their excellent resistance to chemical products and weather. Nevertheless, their insolubility in conventional solvents makes them unusable for certain application such as, for example, that as a resin for paints and varnishes where their properties are sought for the manufacture of coatings with good chemical and weather resistance and easy maintenance.
In order to profit from the desirable properties of the fluorinated polymers while avoiding their drawbacks, means were sought to make them soluble in conventional organic solvents. In order to achieve this, it is known to decrease the crystallinity of fluoride-containing polymers by copolymerization of monomers unsaturated in the ethylene position, of which monomers at least one is fluorinated.
In addition, to use such copolymers it is desirable for certain applications, particularly for their application in the manufacture of paints and varnishes, to preserve for them a sufficient degree of rigidity and to make them hardenable by incorporation of functional groups into their structure.
Such hardenable, fluorinated copolymers are described in French Patents 2,597,873 and 2,569,703. These products are obtained by copolymerization of chlorotrifluoroethylene, a fatty acid ester, and hydroxylated or ethoxylated allyl glycidyl ether. These copolymers can possibly contain less than 20% of another, non-fluoride-containing comonomer. If these copolymers contain more than 20% of the preceding comonomer, they lose their solubility in solvents and their transparency. In addition, the introduction of fluorine by the use of chlorotrifluoroethylene alone also brings with it the chlorine-containing element which is not desirable in large amounts for the optical properties and resistance to corrosion.
In JP 59-174,657/84, there is also described a hardenable copolymer based on vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, a vinyl ester and a hydroxylation agent. This copolymer, which contains less than 45% of vinyl ether fluoride and is based on vinyl ester, has the drawback of yielding after hydrolysis a rather strongly colored copolymer solution, which damages the transparency of the subsequently prepared varnishes.